This invention relates to a seal assembly for sealing about an axis of rotation, more particularly to such an assembly which includes a pair of seal rings mounted for rotation of one relative to the other coaxially about the axis, one of the ring being yieldably pressed against the other with their opposed faces forming the seal. Commonly, the assembly is used to seal the tubular spaces between a shaft and structure surrounding the shaft, one of which, usually the shaft, is rotated about the axis, whereas the other is fixed, the seal rings being respectively connected to the shaft and to the structure to complete the sealing.
Such seal assemblies are often exposed in use to temperature extremes which cause considerable expansion or contraction of the metal or other material of which the parts are made, the amount of expansion/contraction differing with parts made of different materials having different coefficients of expansion. Expansion can be accommodated by spacing of parts which do not have to be clamped or sealed together. However, one of the seal rings needs to be clamped against displacement longitudinally of the axis under the opposed resilient pressure of the other seal ring, and normally also to be sealed to at least one clamping component. This clamped seal ring is commonly referred to as the "hard face," or "mating ring," because its seal face, and usually its entirety, is made of tungsten carbide or equivalent, which is harder than the carbon of which the resiliently pressed seal ring is normally formed and is referred to hereinafter as the "hard seal ring".
In prior art structures, the mutual, differential expansion/contraction of the clamped portion of the hard seal ring and of the clamping structure (which have substantially different coefficients of expansion/contraction in response to temperature changes) has caused serious problems, such as breakdown of the gasket sealing and/or distortion of the seal ring so that its seal face is twisted out of the desired radial plane of engagement, with the consequence of ending, or drastically reducing, the useful life of the seal rings and/or gasketing, necessitating costly shut-down for replacement.